Art of making maps from photographs



Jan. 24, 1933. 1.. J. R. HOLST ART OF MAKING MAPS FROM PHOTOGRAPHS FiledMay 15, 1926 5 Sheets-Sheet 1 Jan. 24, 1933. L. J. R. HOLST ART OFMAKING MAPS FROM PHOTOGRAPHS 5 Sheets-Shee t- 2 Filed May 15, 1926 Jan.24, 1933.

L. J. R. HOLST ART OF MAKING MAPS FROM PHOTOGRAPHS Filed May 15, 1926 5Sheets-Sheet 3 haw/Z127? Jan. 24, 1933. 1.. J. R. HOLST ART OF MAKINGMAPS FROM PHOTOGRAPHS Filed May 15, 1926 5 Sheets-Sheet 4 Jam-'24, 1933.1.. J. R. HO LST 1,894,953

' ART OF MAKING MAPS 'FROM PHOTOGRAPHS F iled May 15, 1926 5Sheets-Sheet 5 ir'kim llllllllllk Patented Jan. 24, 1933 UNITED STATESLODEWYK J. 3. Hour, or naooxnmn, rmmsnvma ART OF MAKING MAPS FROMPHOTOGRAPHS Application filed Kay 15,

As no dependable means to stabilize aerialcameras in a horizontal planehas, as yet, been found various methods to determine the plane ofprojection either by computation or by empiricalmethods havebeen'proposed.

According to the methods heretofore in use computation of the plane ofprojection requires knowledge as to the orientation and the relativeelevation of at least three ground points occurring in each view,thus/necessitating a considerable amount of instrumen-' tal surveyingthroughout the photographically surveyed area in addition to thelaborious and diiiicult work of the computation itself.

The empirical method requires only the knowledge of the relativeelevation of four points in each view and consequently requires muchless field work than other methods heretofore employed but depends forits 39 practical success largely on the experience of the operatorhandling the correction projectors and other special apparatus used inconnection with said method. However, the chief drawback of theempirical method is that it does not provide ready means where by theinfluence of lens elevation difference on the observed errors can bedifferentiated from the influence of tilted projections whenever boththese errors are present si- 0 multaneously. I

The purpose of my invention is to provide means whereby theseshort-comings or difficulties-are obviated by a suitable arrangement ofa plurality of cameras having a common focal planeand associated partsof an aerial camera structure and by the use of a new and novel tiltindicating instrumentality in which optical properties imparted by thecameras of the camera structure to views exposed simultaneously thereinpermit the me- 1926. Serial No. 109,257.

chanical determination in each view of the point where a vertical linethrough the lens pierced the common image plane at the instant ofexposure.

Knowledge of the position of this point (which will be referred tohereinafter as the point p), furnishes complete information as to theposition of the plane of projection or image plane, and consequentlysuch views or images can be re-projected so as to produce the trueequivalent thereof in a horizontal view from the viewpoint of theoriginal tilted exposure. Such knowledge also furnishes information asto the true base length be" tween adjoining views or images and as tothe true flying line, so that the correct center of projection therebybecomes available for the making of the plotted photographic traverse,which constitutes the framework upon which the orthographically. drawnmap finally is constructed,

A general object, therefore, of the invention is to provide a method aswell as means for carrying out the method, whereby the results as aboveindicated may be obtained without the necessity of an instrumentalsurvey in the field to be photographed and of which a map is to bereproduced from the said photographs,

It also is an object of the invention to provide mechanical meanswhereby the image plane of the camera (which is the image surface of thecamera plate) may be placed in position identical with that which itoccupied at the moment of exposure, except as to altitude, so that theimage thereon may be reprojected onto a horizontal plane to produce acorrect image in conical projection of the area shown in the view orimage.

The only field information required in the practice of my invention is asuitable distance measurement to allow the determination of the exactscale in which the map is to be drawn, but if dependable altitude gaugeswere or should become available to aviators, even this distancemeasurement could be dispensed with.

I shall now proceed to a description in detail of my invention in whichI shall point out the method or manner in which the same axis O a ma becarried out and the principle upon which it is based. In order that theinvention may be more readily understood I shall refer in thedescription. to the annexed drawin forming a part of this specificationand v1n which--' Fig. 1 is a schematic perspective view showing orindicating an image plane X having a lens axis a O meetin at the point 0a vertical Blane P p a V whic rests on or intersects a orizontal planeF;

Fi 2 is a diagrammatic view of a horizonta ima e plane and a tiltedimage plane, the former bemg shown by dash lines and the latter by asolid line,'both having a viewoint O in common, the planes intersectinin a line indicated by the point M at equa distances from the opticalcenters of the respective images;

Fig. 3 is a diagram illustrating or indicat: ing a focal plane X andits'lens axis 0 c standing in a perpendicular O P and the slanting ray AO forming an image point at a Fig. 3" is a similar diagram, a doublereflecting prism Q, being shown in position intermediate the viewpointor center of the lenses of the camera and the image plane with itsreflecting surface parallel to the lens illustrating the manner in whichthe ray A 6 of Fig. 3 is reflected to a'point a in a focal or imageplane Y at a distance 0 a which is equal to but in reverse direction tothe distance 0 a in Fig. 3; a

Fig. 4 is a diagram in plan view of the focal or ima e planes X and Yshowing the location of the centers of each plane and of the imagepoints a and a when the said planes occupy horizontal positions;

Fig. 4 is a diagram of the focal or image lanes X and Y with the tracesT T and 1 T as they appear 'respectivelgoin either image plane when thelens axes of are inclined to the extent shown by the lines 0 c and O 0which are the projections on the image planes X and, Y after rotationabout an axis corresponding to the line vO a of Fig. 3, andalso-illustrating how the trace T T of a vertical plane parallel to thever-. tical plane T T before entering the prism Q is twisted by thatprism after emergence g IG IFfIOm so that it extends in the directionFig. 5 is a diagrammatic plan view of one form of structure comprisingthree cameras, with each of two of which is associated a doublereflecting prism Q, the said two last mentioned cameras being regardedand designated as auxiliary cameras, while the other of the said camerasis regarded and designated as a p incipal camera, the said view alsoindicatng the principal focal or'image plane X of the said principalcamera and the auxiliar focal or image planes Y and Z of the auxi iarycameras;

th planes Fi 6 is a diagrammatic elevational sections. view on the ins66 of Fig. 5

Fig. 7 is a view in front elevation of atilt indicator by means of whichthe exact position, except as to altitude, of the focal or image planeof the camera at the moment of ex osure may be determined;

1g. 8 IS a top plan view of the said indicator cipal focal or ima eplane X o the camera views being lined up in structure, the sai correctalinement for stereoscopic observation and contour measurement and draw-Tn Fig. 1 the line 0 0 represents the lens .axis, the point 0 being theviewpoint or point of the lens system from which-the view or image isprojected onto the upper image surface X which is normal to the axis 0 cof the lens system of the principal camera structure. The line m m isthe longitudinal center line of the principal image surface X and thepoint a, located .in this line, is determined by the intersection of theline m m. with the imaginary line m m drawn through marginal markingsformed as a part of the image and being images of markings upon theaperture of the camera. The vertical line P O p asses through the viewoint or lens center 8 and pierces the plane in the point p, which is theimage point of the ground point P of the vertical line P O through theviewpoint or lens center 0.

The line a V represents a vertical dropped or drawn to the groundthrough the point a. As the view oint or lens center 0 lies in thevertical Kno l and as the int a lies in the vertical line a the ray 0 aies in its entirety in the vertical lane determined by these twovertical lines a and P p. Consequently the object A, of which the pointa is the ima must also lie in this vertical plane. As t e ima 0- pointsa and are located in the principa image plane as well as in the verticalplane P p a V the line a'P constitutes the direction of the trace T T ofthese two planes. The downward continuation of the lens axis 0 Oconstitutes the locus for the ground point C. Consequently the triangleformed by the image points a a and p is the image of the actual triangleformed by the ground ints A C and no matter what the re ative grandelevations of these points may happen to The camera structure, which ismore fully described hereinafter, furnishes exposures or ima es in eachof which the points a and can located by means of the marginal markingsm to m", and the viewpoint or lens center O, which bears a fixed andunchanging position with respect to the said oints a and c, is therebymade known so that 1t is possible to support each view or image plane insuch position that a vertical plane cutting the same contains onevertical line' which passes through a and one which passes through theviewpoint or lens center 0, so that a line 0 a will lie in the saidvertical plane. It remains to determine, however, how much the said viewmust be rotated around the line 0 a as an axis of rotation in order thatit shall assume with relation to the vertical plane so established thesame position it occupied at the instant of exposure at which time theimage was formed. Such determination may be efiected and is madepossible by means which are diagrammatically illustrated in Figs. 3and?) of the drawings.

in Fig. 3 the point 0 represents a viewpoint; that is, a center point ofthe lens system of a camera located vertically above the ground point P,and A is an object the image of which isrepresented at a. The lens axis0 c is in the vertical line P 0 and consequently the focal or imageplane X is in a horizontal position. In Fig. 3* a prism Q of the doublereflecting type is shown with the lens axis indicated by O c passingtherethrough. The said prism is so positioned that the emergent part ofthe axis Q a of the lens axis is in true alinement with the incidentportion thereof 0 Q The ray A O. is the same as the ray A O in Fig. 3and enters the prism at the point Q This ray is refracted, as indicated,to a point on the reflecting surface Q of the prisms from which point itis reflected to the point Q at the upper end of the prism and emergesfrom that point in the direction Q a. The line Q a makes the same anglewith the lens axis 0 c as is made therewith by the ray 0 a in Fig. 3 butin reverse position with respect thereto; that is, the image point aoccupies a position spaced 180? from the position of the image point a.As the angle between rays before and after passing through the prism hasnot changed in magnitude the size of the image formed by such rays willbe identical with the image as formed or as it would be formed in theabsence of the prism. But where the prism has been employed it will befound that the focal or image'plane has receded, as compared with thefocal or image plane in Fig. 3 where there is no prism present, by anamount depending upon the index of the prism glass and the size of theprism. v

If two cameras be joined together with their lenses in the samehorizontal plane and a double reflecting prism, such as described, beplaced above the lenses of one of the said cameras and in the axisthereof, a simultaneous exposure of the plates of each camera willresult in the formation of two image points of an'object, such as theobject A, in

cated by the reference letter X, while the focal or image plane of thecamera with which the prism is associated is indicated by the referenceletter Y. In the focal or image plane X the image of the object A willbe found in the point a and in the focal or image plane Y the imagepoint of the said object A will be found in the point (L The distancesof these points from the centers 0 and c are the same butin oppositedirections, as has been indicated hereinbefore.

v A further property or characteristic of a double reflecting prism isthat upon rotation it causes images which are formed by rays which passtherethrough to rotate through angles twice as great as the angles ofits own or actual rotation. This fact is illustrated in Fig. 4 of thedrawings. In this figure it is assumed that the lens axis 0 c has movedout of its vertical position by rotation around the light ray 0 a sothat the length 0 c on the focal or image plane X in said Fig. P will beor constitutes the projection of the tilted lens axis 0 c in the saidfocal plane X. The angle through which the lens axis 4) c has rotated isrepresented by the angle O a c, as shown in plan in Fig. 4 Recallingthat the line 0 a has been considered as the axis of rotation and thatit has not been displaced, it will be clear that the line T T whichpasses through 0 and a is the trace or line of intersection of thevertical plane containing the agxis O a with the tilted focal or imageplane .1 I

Since the focal or image plane Y is rigidly connected with or joined tothe focal or image point a, corresponding to the image point a,

will be found in a line T T deviatmg by an angle 2 O a 0 from thedirection T T parallel to T T upon the focal or image plane X withrespect to the line m m This angular relationship constitutes the meanswhereby I am enabled to correctly reconstruct the relative positions ofthe vertical plane P p a V. with res ect to the focal or image planes Xand Y. l t should be noted that the use of a double reflecting prism inthe manner heretofore explained 1n association with the lenses of one ofthe cameras results in indicating the relative position of the centerline m m of the exposure in the image plane X with-res ct to the trace TT of a vertical plane wh1c contains the lens vertical P 0. However, thisis not suflicient to enable the actual location of the point p to bedetermined because the focal or image plane X can be turned from ahorizontal position around an axis at right angles to the plane P p a Vwithout changing the location of its trace with this plane. Therefore itbecomes necessary to provide a second auxiliary camera with itsauxiliary focal or image plane Z and a second double reflecting prismarranged in right angular relation with respect to the focal or imageplaneY so as to yielda second tracefl T passing through an image point6. The image point 6 is located at a point arbitrarily selected on thetransverse mld line m m at the point of intersection of said line withan imaginary line m m. .Preferabl and in ractice the image point bshould .selecte at apoint in the mid line m m the same distance from thepoint a as is the point a' from the said center a. By thus locatin theimage points a and b the same distance rom the point a the operation ofdetermining the positionin space of the image plane at the moment ofexposure with respect to a horizontal plane is sim lified. (Fig.11.)This traceis determine by another plane containing the lensperpendicular P O to determine by the intersection of the two traces soproduced the actual location of the point p.

The camera structure which is used in the practice of my invention isequipped with three cameras, two of which include double reflectingprisms associated with the lenses thereof, which cameras may be referredto as auxiliary cameras, while the other camera is" not provided withsuch a prism and is referred to and regarded as the principal camera.

Before proceeding with a more or less detailed description of thecameras and the lenses I shall refer to Fig. 2 which consists of themid-point, is in a horizontal plane at the same distance from p (whichin this plane coincides with the point where it is pierced by the lensaxis) as it is in the tilted plane from a, the latter indicating thepoint Where the lens axis pierces the full line tilted image plane. Thisfact holds true for any degree of inclination of the lens axis 0 c asthe'line O M is the symmetry line of the figure. The point Mconsequently is the only image point in the plane of tilt which has notbeen dis-' placed relative to the point a b the tilting of the imageplane, since it is t e only image point which is situated in both thevertical plane 0 p c and the horizontal and tilted lmage planes. Whenthe tilt is reduced to This angle and as that angle is always smallunderstood that my present invention is based upon two geometrical.propositions namely, first,vthat there always is one and only onevertical plane which can be made to contain two points not situated inthe same vertical line, namely, the point O and a; and

second, that any flat surface is determined by three points not locatedin the same straight line, namely the ints O a and c.

It is further to be note that in arriving at the actual position of thecamera'and of the planes of the surfaces of the plates upon which theimages are formed at the instant of exposure, I have had norecoursewhatso-,

ever to known orientation or elevationof any ground point appearing inthe views or images, but by means of my invention the position of thecamera and of the image plane at the moment of exposure is determinedfrom information contained in the images themselves. g

It is to be noted also that the purpose of my invention may beaccomplished by locating the double reflecting prisms of the auxiliarycamera structures below the lenses of such structures instead of in theimages aces of the said cameras. above the lenses. pti-' cally theresults are precisely the same and for some pur see this suggestedarrangement offers a vantages inthe design of the camera.

The frame L of the camera structure, as shown in Fig. 5, is divided intothree main sections. The largest of these sections is 00- cupied b thelenses designated as O in this figure w ose focal or image planeis'that' which hereinbefore has been referred to as the principal imageplane X and the plate magazine L. This section also contains operatingmechanism which however forms no part of the present invention and forthat reason is not shown. 7

The lenses designated 0 and O' of what has been referred to heretoforeas the auxiliary cameras are located in the smaller sections of theframe or'body L at equal distances from the lenses 0 of the principalcamera. This permits the construction of the tilt indicator to besimplified. However, there is no theoretical condition which requiresthat these distances shall be equal. It is preferred that the lenses 0,O and 0 shall 6 be located in lines or planes arranged in right angularrelation to each other, the principal lenses 0 being located at theangle formed by the meeting of these lines. This is the arrangement whenthe structure is viewed in 10 plan. However, this arrangement is amatter of convenience and not a necessity.

The lens of each of the two auxiliary 'cameras with viewpoints O and Ocooperate with a double reflecting prism Q (Figs.

5 and 6). The reflecting surface of the prism the reflecting surface oft associated with the lens of the camera having the viewpoint O isparallel with the plane including the axes of the cameras having theviewpoints O and 0 respectively; whereas e prism cooperating with thelens of the auxiliary camera having the viewpoint O is fparallel withthe plane including the axes o the cameras havmg the viewpoints O and 0respectively.

The apertures of the auxiliary camera structures which are located inthe focal or image planes Y and Z of the two auxiliary cameraspreferably are equal in size, but also preferably considerably smallerthan the aperture 0 in the'principal camera structure which is locatedin the principal focal or image plane X of that structure. This is a(possible arrangement because the images pro iliary cameras need not belarger than may be 5 rcqulred to contain the images of the objectsdepicted in the points a and I) previously explained and as projectedthrou h their respective prisms. Furthermore, y reducin the size ofthese auxiliary cameras the'bul a and weight of the camera structure asa whole is reduced and kept within reasonable limits. The apertures ofthe camera structures which are located int-he focal or image planes Yand Z are closed by flat glass plates Y and 5 Z which'are provided withlongitudinal and traverse center lines which have been carefully etchedand filled in so that they may be photographically reproduced in thepictures produced by the auxiliary cameras for Q purposes which will bedescribed fully in the description of the tilt detector. The exposureaperture located in the'focal or image plane X is provided with marginalmarkings corresponding to the markings m to m 5 shown in the diagrams ofthe focal or image planes heretofore referred to to indicate the opticalcenter and the location of the oints a and b in the principal image asherein efore explained.

0' For constructional reasons the focal or image planes X Y Z preferablyare located in the same plane, hence the lens 0 of the principal camerastructure is located 1n 8. plane extending transversely through thecamera structure above the plane in which uced by the.aux-

the lenses of the auxiliary lens structures are located. This isillustrated in Fig. 6.

A camera structure of the character described embodying my inventionshould be provided with a release mechanism for the shutters, which isdesigned to release the shutters of the three cameras simultaneously inorder that the exposures may be made simultaneously. Any suitablerelease mechanism maiy be employed.

n the use of the camera I preferably employ roll films for the auxiliarycameras because in so doing the sequence in which these small exposuresfollow each other cannot be lost, but the employment of such films isnot an essential condition for the achievement of the purposes of myinvention and consequently any other suitable sensitive film or platemaybe employed without departing from the principle of the invention.

I shall now proceed to describe the tilt detector, which is illustratedin Figs. 7 to 11 inclusive of the drawings, and which is adapted to beemployed for the purpose of ascertaining the exact position of theprincipal image surface or plane of the plate of the camera at themoment of exposure. In the said detectorv means is provided forsupporting the plate of the principal camera and the film or plate ofone of the auxiliary cameras with the image planes or surfaces thereonin exactly the same relative positions that they occupied in the camerastructure. In other words, these planes or surfaces upon the plates orfilms occupy exactly the same relative positions in the detector devicewith respect to each other as the focal planes X and Y and X and Zoccupied with relation to each other at the moment or instant ofexposure. The negative plates of the principal camera and the auxiliarycamera Y are shown at X and Y respectively, in Fig. 8 of the drawings.The plate X is supported upon a turn table X within which an opening oraperture is provided over which the plate X extends, as is clearly shownin Fig. 10 of the drawings. The turn table is pro vided with a couple ofnotches X formed in the peripheral edge thereof with which notches aspring actuated lock c'atch X is adapted to engage to lock the turntable in either of two positions in right angular rela tion to eachother. By this means the plate X can be placed in such position withrespect to the aperture over which the negative Y is located as shown inFig. 8 of the drawings that the negative bearing the focal plane orimage surface Z of the camera 0 shown in Fig. 5 when substituted for thesaid negative Y will occupy the same relation with respect to thenegative plate X as is shown in Fig. 5 and as it occupied at the momentof exposure when the images upon the three plates or films of thecameras were formed.

By providing means which enables the su port; consistm of the turn tableX, to e rotated throug an angle of 90 so as to roduce a 90 change in theposition of the ate X, I am enabled to employ a single tilt indicator ordetector for comparing both of the negatives of the auxiliary cameraswith the negative of the rincipal camera for the determination of t etraces of both of the auxiliary vertical planes. The ability to adjustthe turn table as stated avoids the making of different adjustments ofthe negative X thereon. It may be noted that the aperture in the turntable is provided with a series of notches therein designated M whichcorres 0nd to the notches m to m appearing in t aperture of the cameraand which have been imaged upon the negative X. In mounting the negativeplate X upon the turn table it is ositioned with respect to the aperturetheret rough so that the markings m to m thereon coincide or correspondwith the notches M in the edge of said aperture. The negative plate X isheld in that osition by means of adjustable lock bars which are mountedupon the turntable and may be adjusted so that inwardly extendinprojections at the opposite ends thereo contact with the edges of thesaid plate so as to Drevent displacement thereof in any direction in itsown plane. Additional holding means for the plate are provided whichconsist of spring pressed plungers M.

A support or holder H is provided for supporting the negatives producedby the auxiliary cameras. It consists of a plate projecting from oneedge of the top plate of the frame L of the tilt indicator or detector.The said projecting supporting plate H is provided with an aperture overwhich is mounted a glass late H upon which the negatives produce by theauxiliary cameras are ada ted to be su ported. The negative Y pro ucedupon the camera 0 that is, the camera shown at the lower side of Fig. 5of the drawings, is'shown in Fig. 8 as being mounted u on the said plateH The said glass plate is provided with cross lines etched therein withwhich the corresponding photographically reproduced lines of theauxiliary images are placed in registr The etched lines in the saidglass late H are so placed with respect to the mar ings M in theaperture of the turntable that when the negatives of the auxiliarycameras are placed on the said plate with the photographicallyreproduced lines in registry therewith the said negatives occupy exactlythe same position with respect to the negative plate X as that obtainedbetween the negatives in the camera structure.

The negatives when placed upon the glass plate K may be held in positionthereon by placing thereover a plane sheet or plate of glass.

memes ends of two links K are respectivel pivoted. v

The outer free ends of these lin extend between and are guided by. asecond set of lugs K rovided at the outer ends of the said lever. nivesK of sickle or ri ht an ular shape are ivoted to the outer ree en s ofthe links the pivots extending throu h openings in the handle portionsof t e knives and the opposite ends thereof extendmg into iding slots Hin the rojections K. The nives K are provided in the portions thereofbetween the ri ht an larly related handle and blade portions with curvedslots H through which the pivots for connecting the links K to theprojections K extend. These slots permit vertical movements of the innerend ortions of theknives. The upper ends of t e vertical portions of thekmves K are ground to sharp edges. As shown in Fig. 9 these edges areformed by grinding one side of the u per end portionsv of the verticalparts thereo By thus ding the knives they may be sha ned y regrindingfrom time to time wit out changmg the positions of the cuttin edgesthere of with respect to the vertical iane in which the said edges arelocated. One of the lugs K on the shorter arm of the lever K, as shownin Fig 10, is provided with an upward extension K upon which is mounteda roller K which contacts with the under side or surface of the turntable X. The said roller is held at all times in contact with the underside of the said table as a result of the tension of a spring K and thelever K at all times in parallel relation to the turn table. 7

The bracket K previousl referred to is supported on the base plate insuch position that the lane in which the cutting edges of the knives arelocated and in which they operate coincides with the vertical planewhichincludes the slanting axis of the rotatable shaft support L uponwhich the frame L and other parts of the structure as shown aresupported. The said axis corresponds to the line 0 a previously hereinreferred to.

The cutting ed es of the knives K are adapted to be hel out of contactwith the bottom surface of the negative plate X by means ofspring-pressed catches K which are ada ted to engage pins which projectlaterally mm the said knives at points adjacent the angles between thehorizontal and vertical portions thereof. The catches K are mounted uponthe lever K Springs K which are located between the lever K and theinner ends of the knives K operate upon release pf the catches K toelevate the knives into position with the cutting edges thereof incontact with the lower side of the negative plate X When the cutting edes of the knives are in contact with the un er side of the late Xdepression of the outer ends of the andles thereof will cause pivotalmovement of the said knives to form scratches or marks in the/emulsionupon the under side of said plate near the op osite edges thereof inline with the trace 0 the vertical plane through the axis of the pivotpin L (corresponding to the line or axis 0 a previously referred to;1with. the plane of the'image surface of t e plate no matter whatposition thp latter may occupy with respect-to the said axis.

The frame L is provided with a suitable support L within or upon whichthe prism Q, is supported. The said prism is supported in properposition underneath the negative plate or film Y previously referred to.The relative positions of the prism Q, and the negative or film Y arethe same as that which existed between the corresponding prism and thefilm or plate in the auxiliary camera. The prism Q and the frame L arerigidly joined or connected together so that any turning motion impartedto the frame will cause a corresponding turning motion of the prism.

The slanting or inclined pivot pin or support L previously referred tois mounted in an inclined opening through a-block L The said blockis'provided with a centrally located projecting portion, as shown inFig. 10 of the drawings, the upper surface of which occupies a planewhich extends at right angles to the axisv of the said pivot pin orsupport L The said surface forms a thrust hearing or thrust surface forthe hub of a worm wheel L which is keyed to the said pivot pin L Theupper end of the pivot pin L is reduced in diameter, as indicated, so asto provide a shoulder upon which is supported a disk designated as awhole as L. The upper surface of the said disk lies in a plane parallelwith the plane of the turn table X The frame L and disk L are soconstructed that the vertical distance from' the point 0 shown in Fig.10 (which corresponds to the viewpoint O of the lens system of theprincipal camera previously referred to) to the center point of the topsurface of the turn table X is equal to the focal length of the lens ofthe principal camera of the camera structure. The point 0 is located atthe intersection of the vertical line therethrough and the line 0 ashown in Fig. 10 and represents the location of the second nodal pointof the lens or lens system of the principal camera of the camerastructure. For the purpose of eifecting rotation of the worm wheel Ltogether with the pivot pin L and parts supported thereon I haveprovided a worm L" mounted upon or formed upon a shaft L. A hand wheel Lis provided u on Y the line or axis 0 a. The said pivot posts arelocated in the same vertical plane as the axis of'the pivot pin orsupport If or with the axis line 0 a. For the purpose of effectingpivotal movement of the levers N and N about their ivots I have provideda radial lever N wh1ch is mounted upon and kc ed to the hub of the wormwheel L so that w on the latter is rotated the arm is likewise rotatedand a link N one end of which is connected to the outer end of said armand the other end of which is connected to an arm S formed by anextension of one of the levers N or N In the construction as illustratedthe arm S constitutes an extension of the lever N I have provided a lampbox N the opposite ends of which are connected by means of bars N to theouter swinging ends of the parallel levers N and N. The bars N havepivotal connection with the levers N and N The combined length of thelamp box and the bars N is such as to hold the levers N and N inparallel relation to each other. I

The upper surface of the lamp box is provided with a narrow slot Nthrough which the light emitted from a straight filament shines in avertical upwardly extending plane. The inner edge of the said slottoward the pivot pin L is located so that it occupies a position inexact parallel relation to the vertical plane which includes the axis 0a (as shown in Fig. 10) and at a distance from said plane which equalsthe distance from the centers or viewpoints of the lenses of theauxiliary cameras to the center or viewpoint of the lenses of theprincipal camera in the lens structure previously referred to. For thepurpose of shielding the light through the slot N I have provided ashield N which is located inwardly of the said slot, as shown. The saidshield is provided with a flange which extends outwardly and which isparallel with the upper or top surface of the lamp box N and the outeredge of which is located in exact vertical alinement with the inner edgeof the slot N. In other words, the outer edge of the flange of the saidshield is located in or is included within a vertical plane whichlikewise includes the inner edge of the slot N. As a result of thisarrangement-a vertical beam of light is caused to be sent 'throu h theprism Q mounted in the holder L t e inner edge of which beam cuts theimage surface of the negative film or plate Y. shownin Fig. 8 in a traceor along a line parallel to the plane through the line 0 a shown in Fi10 which is coincidental with the axis of the pivot pin or support L.

Upon rotation of the frame or body L of the tilt indicator or detectorto effect rotation or change of position of the prism Q and the lam boxN about the axis 0 a the distance o the visualized vertical planeproduced by the beam of li ht through the slot N from the immova levertical plane through the axis 0 (1 remains at all times equal to thedistance between the centers of the lenses or lens systems of theprincipal and auxiliary cameras u on imaginary or real rotation of thelatter a out a corresponding axis or line 0 a. This is due to the factthat the lamp box is supported upon the parallel bar mechanismpreviously referred to.

It will be understood that when the tilt indicator or detector isadjusted into position to support the negative plates or films inpositions representin the image surfaces thereof as occupying ahorizontal lane or horizontal planes at the moment 0 exposure, thereflecting surface of the prism Q in the detector is arranged at rightangles to the direction of the vertical plane visualized by the beam oflight through the slot N of the lamp box N. At such time the inner edgeor surface of the said beam will be or apear in line with the longcenterline of the image surface of the negative plate or film Y. Inother words, the inner edge or surface of the said beam will be in linewith the long center line of the aperture in the support for thenegative plate or film Y and in parallel relation to the vertical planethrough the axis 0 (1 (shown in Fig. 10). Upon rotation of the frame orbody L (upon which the negative lates or films X and Y or X and Z, as te case may be, are supported) about or around the axis 0 a in whichrotation the prism Q participates, the effect of the latter will be toturn the trace of the plane visualized by the beam of light through theslot N with the image plane or surface of the negative plate or film Yor Z, as the case may be,- out of parallel relation with respect to thecenter line of the said image plane. Due tothe presence of the doublereflecting prism Q the angle between the trace of the visualized planewith the center line of the plane or image surface of the negativeplates or films Y" or Z, as the case may be, will be twice as great asthe angle between the fixed vertical plane including the axis 0 a andthe center line of the lane or ima e surface of the negative plate enthe inner side or edge of the light beam passes through the image pointa upon the lens of t the secondary or auxiliary negative plate or film Y(the image point a u n the secondary' or auxiliary negative 1m or platecorresonding to the image point a upon the plate it will be understoodthat a condition has been reproduced in which the relative positions ofthe two vertical planes through the lens centers of the cameras by whichthe plates X and Y were produced are identical with what they were atthe moment or instant of exposure of the cameras to produce such images.After adjustment of the frame or body L so as to reproduce theconditions just stated and while occupying such adjustment the knives Kare operated to place markings upon the under side of the princi alnegative plate X to indicate thereon t e direction of the trace of thevisualized plane with the plane or image surface of the negative film orplate Y.

Heretofore in this descriptionit has been 4 considered that the negativefilm or plate Y has been supported in the auxiliary aperture of the tiltindicating device, the said negative having been produced by theauxiliary camera shown at the lower side of Fig. 5 of the drawings.

The fact that the turn table X may be turned through an angle of so asto place the negative plate X in a position at right angles to that inwhich it is' shown in Fig. 8 has already been adverted to. In otherwords, the turn table may be adjusted so as to change the left hand endof the negative plate X, having reference to Fig. 8 of the drawings,from the position shown into a position in parallel relation to the aerture of the support for the auxiliary fi ms or plates. When this hasbeen done and the negative film or plate bearing the image correspondingto the focal or image plane Z previously referred to is substituted forthe negative film or plate Y, the said plate will occupy the samerelation to the plate X as it occupied in the camera structure.Therefore, it will be seen that the same operation as has been describedin connection with the negative plates X and Y will yield the traces ofvertical planes including the axes through image points I) and b uponthe principal plate X and the auxiliary plate correspondin to the focalor image plane Z c'orrespon ing to the vertical plane through the axis 0a and the visualized vertical plane through the image surface of thenegative film or plate Y as previously described. Since both of thesetraces contain or include the vertical line through the lens center (0in Fig. 10) their intersection will mark a point p, which is the pointwhere the verticalline through thecenter or viewpoint of e principalcamera met the image surfaceor plane upon the negative when the exposurewas made or took place. The ascertaining of the position of the pointcontaining the image thereon in the identi-. cal position it occupiedwith respect to a' horizontal plane at the moment of exposure.-

It will be apparent that by the combined action of the camera structure,including three cameras preferably though not necessarily arranged inrelation to each other as shown in Fig. 5, and the tilt indicator orde-. tector, I am enabled to determine the actual position in space ofthe focal or image plane of the principal camera (as well as of theauxiliary cameras) at the instant of exposure without the necessity ofrecourse to any measurements of ground points which occur in the views.

As soon as two or more overlapping aerial exposures have been marked inthe manner as above described and as diagrammatically shown in Fig. 11,they are ready to be insorted in any known type of correcting projectorand to be adjusted therein so as to yield by reprojection the correctequivalent horizontal view from the viewpoint of the lens of the cameraat the moment of exposure. These horizontalized views are then ready tobe placed in proper alinement in known manner in a measuring stereoscopeas is diagrammatically illustrated in Fig. 12 of the drawings. Thisbrings the points p in each view and their conjugate points in astraight line parallel to the line uniting the axes of the eye pieces ofthe stereoscope.

My invention comprehends both the moth 0d or art of procedure as aboveoutlined as well as mechanical means for ascertaining the exact positionin space of the focal or image plane of a camera with respect to ahorizontal plane at the moment of exposure of the sensitive plate ofsaid camera.

have produced in a camera structure a plurality of images not less thanthree, at a single exposure, the images of points in two or more of thecameras being displaced with respect to the images of the same points ofthe other or remaining camera, referred to as the principal camera,through definitely related angles so as to produce means whereby theimages may be compared to ascertain to me of carrying out or practisingmy in It will be seen that by my invention 1' the angle of tilt of thefocal or image plane means than-that illustrated and by the em-.

ployment of instrumentalities of modified construction without departingfrom the spirit of the invention, as disclosed herein, and that thesteps to be followed may be modified within the scope and principle ofthe invention.

Having herein disclosed my invention, in cluding among other things acombination of mechanical and optical devices whereby the properties ofperspective may be im arted to photographic images which in t emselvesare sufiicient to enable a reconstruction of the true plane ofprojection without the aid of further information derived from groundmeasurements, I hereby claim the same as follows:

1. The art of producing topographic maps of ground areas by means ofaerial photography which comprises the production of a plurality ofimages having a common focal plane, a common viewpoint and all exposedat the same instant, one of said images constituting the principal imageand the others constituting auxiliary images, the said auxility imagesbeing generated by means, including a reflecting surface, causing knowndisplacements of image points in the said auxiliary images with respectto the corre sponding image points in the principal image when theircommon focal plane deviates from a horizontal plane, and thereaftercomparing the relative positions of these several image points todetermine the position in space of their common image plane with respectto a horizontal plane at the instant of exposure.

2. The art of producing topographic maps of ground areas by means ofaerial photography which comprises as steps the simultaneous exposure ofa plurality of cameras having a common focal plane, causing during saidexposures relative displacements of corresponding image points in theseveral images, the said relative displacements being in predeterminedangular relation with respect to certain fixed directions in said focalplane, and thereafter comparing the positions of said relativelydispla'ced image points to determine the exact position of thecommonimage plane with respect to a horizontal plane at the moment ofexposure.

3. The art of producing topographic maps by means of aerial photographywhich comprises as steps the simultaneous production of a plurality ofphotographic images at a single exposure, the images occupying fixedpositions with respect to each other, causing during said exposurespredetermined angular displacements of the image points in all of thesaid images except one, with respect to a selected directionfixed withrelation to the images, thereafter visualizing a vertical plane parallelto a vertical plane including a vertical line toward the ground from theviewpoint of the image in which the image points have not beendisplaced, and a line extending from said viewpoint, which line isangularly related to the said vertical line an which pierces the imagelast referred to, ant causing the trace of said visualized plane withone of the images in which the image points have been displaced to passthrough an image point corresponding to a certain image point selectedin the image wherein the image points have not been displaced and alsocausing the trace of the said visualized vertical plane with the otherof said images in which the imagmpoints have been displaced to passthrough another image point corresponding to another selected imagepoint in the image in which the image points have not been displaced,and indicating upon the image in which the image points have not beendisplaced traces parallel to the traces of the said visualized verticalplane with the.

images containing the said displaced image points, to thereby determinethe exact position of the image plane of the lens of the I camera at themoment of exposure.

4. The art of producing topographic maps of ground areas by means ofaerial photography which comprises as steps therein the imparting ofdifferent perspectives to a plurahty of images produced simultaneously,thereafter associating two of the said images with means for visualizinga vertical plane through the said respective images, the said verticalplane being parallel with a vertical plane including a vertical linefrom the viewpoint of the said images toward the ground and a lineextendingfrom the said viewoint in angular relation to the said verticalinc and piercing an image with which such visualizing means is notassociated, and adjusting the said respective images until thesaidvisualized vertical plane includes both the said vertical line and aselected image point in the respective images with which suchvisualizing means is associated, the said selected image point in one ofthe said images being different from the selected image point in theother of said images, the said visualized vertical planes cutting theplane of the said ly in the same relative positions with respect to eachother that they occupied at the moment of exposure, selecting a point ina center line of the principal image in a vertical plane which alsocomprises the view point from which said ima e was taken, the said planerepresenting a med lane, then causing a beam of light to extendvertically and successively through a corresponding center line of therespective auxiliary images, the plane of the said beam being parallelwith the said fixed plane, thereafter turning the said images aroundanaxis coincident with the slanting line connecting the said pointlocated in said center line of the principal image and a viewpoint ofsaid image, maintainin the visible vertical plane of light through t 1eauxiliary image in parallel relation to the fixed plane, simultaneouslymoving the center lines of the principal and auxiliary images in angularrelation to the fixed and visual vertical planes respectively, causingthe change in the angle between the plane rendered visible by the beamoflight and the center line of the auxiliary image to be twice as greatas that of the angle between the center line of the principal image andthe said fixed vertical plane, and thereafter indicating upon theprincipal image the direction of the trace of the fixed vertical planewith the plane of the principal image.

6. The art of producing topographic maps of ground areas by means ofaerial photography comprising as steps therein the productionsimultaneously of a plurality of negatives of a ground area,therea-ftersupporting said negatives in the same relative positions with respect toeach other-that they occupied at the moment of exposure, visualizing avertical plane whichcomprises a downwardly extending vertical line fromthe "iewpoint from which said negatives were taken and a line extendingfrom said viewpoint in angular relation to said vertical line to aselected point in an image, the said vertical plane adapted to include aselected image point in one of said negatives andanother the exactposition of the image plane of said negatives with respect to ahorizontal plane at the moment of exposure, and thereafter producingfrom one of the said plurality of negatives by projection a horizontalequivalent view thereof in the view point from i which said last namednegative was taken.

7. Apparatus for making maps from aerial photographs comprising meansfor supporting a principal image and a corresponding auxiliary image inthe positions relative to each other which they occupied at the momentof theinforma'tion b exposure, a support for said means mounte to rotateabout an axis slanting with respectto a vertical line and passingthrough a point corresponding to the anterior nodal point of the lens ofthe rincipal image and through a point of that lmage, means to effectvisualization of a vertical plane parallel to the vertical planecontainmg the said axis, said lane so visualized passing through theauxiliary image, means operating upon rotation of said support tomaintain the said vertical planes a distance from each other equal tothe distance between the points corresponding to the centers of thelenses by means of which the said principal and auxiliary images wereformed, the rotation of said support and principal and auxiliary imagessupported thereon around said axis causing an image point in saidauxiliaryimage corresponding to the image point at the point in the saidprincipal image where it is pierced by the said axis to fall in thetrace of the visualized vertical plane and the auxiliary image plane,and means to mark the principal image at such time to indicate thedirection of such trace thereupon.

8. Apparatus for making maps from aerial photographs comprising a tiltindicator having means for supporting a plurality of simultaneouslyexposed photographs in the same position relative to each other thatthey occupied at the moment of exposure thereof, means adapted tovisualize a vertical plane, the said plane forming a trace with theimage plane of one of said photographsand the said indicator also havingmeans to mark the direction of a parallel trace made by a parallelvertical plane with the image plane of another of said photographs. 7

9. Means for making photographic maps of ground areas by the employmentof aerial photographs, one of said photographs constituting a principalphotograph and the others auxiliary photographs, which means includes atilt indicator which comprises a rotatable support for the saidphotographs, means for locating the said photographs upon the saidsupport 1n the same relation to each other that they occupied at themoment of exposure of the negatives thereof, an inclined pivot uponwhich the support for the said photographs is mounted, means forvisualizing vvertical planes through the said auxiliary photographs,means for maintaining the said visual planes in parallel relation to avertical plane through the axis of the said inclined pivot upon rotationof said sup- 'occupied at port about said axis, the principal and auxillary photographs upon suchrotation moving in directions crosswise of thesaid vertical planes so that the angularity of the traces of thevertical planes through the said'photographs with respect to thelongitudinal and transverse center lines of the said photo graphs isvaried, means for causing the variation of the angle of the trace of thevisualized vertical plane with respect to the longitudinal andtransverse lines of the auxiliary photographs to be twice as great asthat of the longitudinal and transverse center lines of the principalphotograph with respect to the trace of the vertical plane through theaxis of the said inclined support with said principal photograph, andmeansfor marking upon the principal photograph the direction of thetrace of the visualized vertical plane with the image plane of theauxiliary photograph at the moment when the image point in saidauxiliary photograph corresponding to the image at the point where theaxis of the said inclined support pierces the image plane of theprincipal photograph comes into line with the visible trace on saidauxiliary photograph.

10. Means for making photographic maps of ground areas by the employmentof a plurallty of aerial images one of which constltutes a principalimage and the others constituting auxiliary images, the said imagesbeing formed simultaneously upon a plurality of sensitized plates heldin fixed relation with respect to each other, which means comprises atilt indicatlng device havin means for supporting a plurality or: sa1plates, one of which is the principal image plate, in the same relativePOSItIOIIS with respect to each other that they occupied at the momentof exposure, said means being rotatable about an axis tilted withrespect to a vertical line, means for adjusting said plates around saidaxis into the os1t1ons with respect to a horizontal plane w 1c h theythe instant of exposure in the camera, means for determining when thesaid plates have been adjusted to such positions, said means including adevice for visualizing a vertical plane including a vertical line fromthe viewpoint from which the images were taken and the said tilted axis,so that it may be ascertained when the trace of the said vertical planewith the plane of said auxiliary image pass-es through an image pointthere n corresponding to a selected image point in the principal image,and-means for narklng the principal image plate when in such position.

11. Apparatus for making maps from aerial photographs comprising plateshaving .thereon principal and auxiliary images, the

said principal image including image points which are duplicated in theauxiliary images, the positions of the said image points in theauxiliary images being shifted withres'pect to their positions in theprincipal image in goniometrical function of the tilt, means forsupporting the principal image plate and an auxiliary image plate infixed relation to each other, means for rotating said supporting meansabout an axis tilted with respect to a vertical line, and meansincluding a device for visualizing a vertical plane through saidauxiliary images parallel to a vertical plane including said tilted axisand a vertical line toward the ground from the viewpoint from which thesaid principal image was taken for determining when the said plates havearrived at positions occupying the same relative position with respectto a horizontal plane as that which they occupied at the instant ofexposure to reduce the images thereon.

12. A tilt indicator for use in the making of maps from aerialphotographs comprising means for supporting principal and auxiliaryimage plates in fixed relation to each other, a rotatable support forsaid means, the axis of said support extending. at an acute angle to avertical line extending toward the ound from the viewpoint from whichthe rmcipal image was taken, means for determining the trace of avertical plane through an auxiliary image plate including an image pointof a certain ground point, said plane being parallel to a vertical planeincluding the said axis and a vertical line extending toward the groundfrom the viewpoint from which the said principal image was taken, andmeans for marking the trace upon the principal image plate of a parallelvertical plane including therein the image point of the same groundpoint.

13. Apparatus for producing maps from aerial photographs which comprisesa device for ascertaining and determining the tilt of the image plane ofa photograph at the instant of exposure, which device comprises meansfor supporting a plurality of images in the same relation to each otheras that which they occupied at the instant of exposure, a rotatableshaft for supporting said image-supporting means, the axis of said shaftextending at a predetermined acute angle with respect to a vertical linefrom the viewpoint of the lens system of one of the cameras by whichsaid images were produced and being inclined with respect to the planeof the said images, and means for determining when the said imagesoccupy positions upon the tilt-indicating device in a plane having thesame angular relation to a horizontal plane as that in which they werelocated at the instant of exposure. a

14. Apparatus for producing maps-from aerial photographs which comprisesa device for ascertaining and determining the tilt of the image plane ofa photograph at the instant of exposure, which device comprises meansfor supporting a plurality of images in the same relation to each otheras that which they occupied at the instant of exposure, a rotatableshaft for supporting said image-supporting means, the axis of said shaftextending at a predetermined acute an c with res to a vertical line fromthe viewpoint o the lens system of one of the cameras by which sa dimages were produced and being inclined with respect to the lane of thesaid images, means for rotating t e supporting means for said imagesrelatively to each other, and means for determining when the said imoccu y positions u n the tilt indicati evice in a plane havi g the sameangulai relation to a horizontal plane as that in which they werelocated at the instant of exposure. 15. Apparatus for makin maps fromlmages simultaneously ex the sensitive lates upon which the said imagesare ormed supported at the moment of exposure 1n fixed relation to eachother, one of'sald nnages constituting a principal image and the otherimages constituting auxiliary 1ma es, the said apparatus comprisingrotata 1e means for supportin the said ima es in the same positionsrelative to each at erthat they occupied at the moment of exposure, theaxis of rotation of the said support belng inclined with respect to avertical line including the viewpoint of the principal images, means forcausing rotation of said support about the said inclined axis to causethe lane of said images to assume positions 1n p anes having differentangular relations to a horizontal plane, a device for visualizing avertical plane through the auxiliary images parallel to a vertical planeincluding the vertical line from the viewpoint of the said principalimage and the said tilted axis, and means for indicating upon the saidprincipal lmage traces parallel with the traces of the said visualizedvertical plane with the said auxiliary images.

16. Means for making photographic maps of ground areas by employment ofaerial images, the said images being formed simultaneously upon aplurality of sensitized plates held in fixed relation with respect toeach other in acommon focal plane, one of which images constitutes theprincipal image and the others auxiliary images, which means comprises,in combination, a rotatable support for supporting the said plates withthe images thereon in the same positions relative to each other thatthey occupied at the instance of exposure, the said support beingrotatable about an axis inclined with respect to a vertical lineincluding the viewpoint by through the auxiliary images, and means formaintaining the said plane in parallel relation to a vertical planeincluding the said axis ,sure, the said means includin amps:

and a vertical line including the viewpoint of the rincipal imagp.

17. cans for ma 'ng photographic maps of ground areas by the employmentof three aerial images, the said images bein formed simultaneously in acommon focal p ane, one of which images constitutes the principal imageand the other two auxiliary images, which means comprises a support forsupporting the said images in the same relation to each other as thatwhich they occupied at the moment of exposure, the said support beingadjustable about an axis inclined to a vertical line including theviewpoint of the primary image means for adjusting the said supportaround the sald inclined ax1s so as to var the angle of the planeoccupied by the sai images to a horizontal plane, means for determiningwhen the said images have been adjusted into a plane having the sameposition with respect to a horizontal plane as that which they occupiedat the moment of expoa device "located underneath an auxiliary 1mageupon said support for visualizing a vertical plane through the saidauxiliary image, and means for maintaining the said vertlcal planeduring adjustment of the said images around the said axis in parallelrelat1on to a vertical :plane including a vertical line through theviewpoint of the said principal 1mage and the said inclined axis. J I V18. Means for making a photographic map of a ground area by theemployment of aerial images, the said images being formed simultaneouslyin a common focal plane, one of which images constitutes a principalnnage and the other two auxiliary images, the auxlliary images being solocated with respect to the primary image that lines drawn from thecenters of the auxiliary images to the center of the primary imageintersect at right anles to each other, which means comprises, 1ncombination, a support for the said primary image and an auxiliaryimage, thesai'd support being rotatable about an ax1s tilted withrespect to a vertical line extending through the viewpoint of theprincipal image, means upon the said support for holdin the saidprincipal image, which means is ad ustable through 90 degrees about anaxis at right angles to the plane of said image so that the saidprincipal image may have the same relation upon said support to the saidauxiliary images that it had at the moment of exposure, means forcausing rotation of said support and the images carried thereby aboutthe said tilted axis, a device for visualizing a vertical plane throughthe said auxiliary images to provide visual means for ascertaining whensaid plane passes through certain image points in said auxiliary imagescorresponding to selected points in the primary image, the said planebeing parallel with a vertical plane including the said tilted axis andone of the said selected points in the to said vertical plane includlngthe said tilted axis.

19. Means for making a photographic map I of a ground area by theemployment of aerial images, the said images being formed simultaneouslyin a common focal plane, one of which images constitutes a principalimage and the other two auxiliary images, the auxiliary images being solocated with respect to the primary image that lines drawn from thecenters of the auxiliary images to the center of the primer ima eintersect at right angles to each ot er, w ich means comprises, incombination, a support for the said primary image and an auxiliaryimage, the said support bemg rotatable about an axis tilted with respectto a vertical line extending through the viewpoint of the principalimage, means upon the said support for holding the said principal image,which means is adjustable through 90 degrees about an axis at rightangles to the plane of said image so that the said prmclpal image mayhave the same relation upon said support that it had at the moment ofexposure to each of said auxiliary images, means forcausing rotation ofsaid support and the images carried thereby about the said tilted axis,a device for visualizing a vertical'plane through the said auxiliaryimages 7 to provide visual means for ascertainng when said plane passesthrough certain image points in said auxiliary images correspondmg toselected points in the primary image, the said plane being parallel witha vertical plane including the said tilted axis and one of the saidselected points in the primary image when the latter occupies oneposition and the other selected point in said primary image when thelatter occupies its other position, and means for indicating upon theprimar image the directions of the traces of sai visualized verticalplane with the said auxiliary images.

2 Apparatus for making maps from aerial images produced uponsimultaneously exposed plates, one of the said images combining aprimary image and the other auxiliary images, the said apparatuscomprising a support for said images, said support havmg means forholding the said images in the same relative positions with respect toeach other as that which they occupied at the momentof exposure, thesaid supporting means being rotatable about an axis tilted with respectto a vertical line through the viewpoint of the primary image, means forcausing rotation of the said support about the said tilted axis toadjust the images into the same plane with respect to a horizontal planeas that which they occupied atthe instant of exposure, a device forvisualizing a vertical plane throu h the said auxiliary images, saidplane ing parallel with a vertlcal plane including a vertical lineextendin toward-the ground fromthe viewpoint o the primary image and thesaid tilted axis to afford visual means for ascertaining when the tracesof the said first named vertical plane pass through certain image pointsthereon corresponding to selected image points in the primary ima e,means for maintaining the said visualize plane in parallel relation tothe said vertical plane including the said vertical line and tilted axisduring the rotation of the said ima es about the said tilted axis, andmeans for indicating upon the primary image the directions of the tracesof the said visualized vertical plane with the said auxiliary images todetermine the position upon the primary image of the image of a groundpoint vertically below the viewpoint of the primary image.

21. Apparatus for making maps from a plurality of images simultaneouslyproduced, one of said images constituting a principal image and theothers auxiliary images, the primary and auxiliary images exposed in thesame viewpoint and the image points in the auxiliary images occupyingdifferent positions with respect to selected directions extending atright angles to each other from those which they occupy with respect tocorresponding directions in the primary image, which means comprises asupport for supporting the said principal and auxiliary images in thesame relative positions with respect to each other that they occupied atthe moment of exposure, the said support being rotatable about an axistilted with respect to a vertical line from the viewpoint of the cameraby which the principal image was produced, the said axis meeting thesaid vertical line at the said viewpoint, means for rotating the saidsupport about the said tilted axis-to cause the images carried by saidsupport to assume positions in difi'erent planes aving different angularrelations to a hori zontal plane, and means operatively related to theauxiliary images when mounted upon said support for determining when thesaid 1 images reach a plane corresponding to that which they occupied atthe moment of exposure. In testimony that I claim the foregoing as myinvention, I have hereunto signed my name this 23rd day of April, 1926.

LODEWYK J. R. HOLST.

